MadSci Network: Biochemistry

Re: how does a TOF reflector work?

Date: Fri Feb 20 08:15:25 2009
Posted By: Luis Sojo, Faculty, Chemistry, Simon Fraser University
Area of science: Biochemistry
ID: 1235103142.Bc

Hi Mei,

The field generated by the reflector (or reflectron) will be penetrated deeper by ions with more energy. The velocity spread, or kinetic energy spread of the ion beam, is due amongst other things to thermal distribution. Each of two isotope isomers (same ions with different isotopic mass) will have its corresponding kinetic energy distribution, and as you mentioned, the ions with more energy will penetrate the reflector field deeper, resulting in longer fly time, but the final result is only seen in the peak width of the particular ion. For example, take the molecule C2H6; it has a mono- isotopic mass of 30 amu. Its positive ion will be 31 m/z and its mass spectrum will show masses at 32 m/z and 33 m/z, because of the isotopic distribution or carbon. a Low resolution mass spectrometer (quadrupole) will be able to distinguish these ions clearly, while a TOF-reflector type of instrument will do so, but the peak width of each isotopic peak would be over 10000 times better. This the result of the reflector narrowing down the kinetic energy distribution resulting on a more even fly time and narrower peak width.


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